An extruder suitable for processing rubber of this general type is disclosed in British Patent Specification No. 960 575. This extruder comprises a feed roller which cooperates with the screw of the extruder in order to achieve a satisfactory supply of strips or pieces of rubber into the extruder.
During the feed operation, rubber adheres to the smooth external surface of the feed roller. The feed roller is, in this known arrangement, driven at substantially the same circumferential speed as the screw. In order to ensure that the rubber adhering to the feed roller remains in the feed section, a stripper blade is used. This is directed against the surface of the feed roller over its entire length and is spaced therefrom by a pre-set gap of from 0.05 to 0.1 mm.
The stripper blade only removes rubber efficiently from the feed roller surface when the point of the stripper blade is not worn, that is to say when the dimension of the gap between the roller and the blade can be maintained constant. If wear phenomena become apparent in the point region of the blade, it is necessary for the blade to be readjusted or replaced. Since the stripper blade is disposed in the extruder housing, considerable difficulties arise if the stripper blade needs to be readjusted.
If the stripper blade is inadequately adjusted relative to the surface of the feeding roller, rubber emerges from the extruder at the end thereof where the feed roller is disposed. In the case of an extruder having a screw diameter of 300 mm and a feed roller having a diameter of 400 mm, up to 100 kg of rubber per hour may emerge from the extruder at the feed roller end in this manner. In consequence, in order to avoid these rubber losses, it is necessary for an operator to readjust the stripper blade very frequently and this must be effected manually.
Since the feeding of the strips or pieces of rubber produces constantly changing separation forces between the screw and the feed roller, the pressure of the rubber acting on the stripper blade, is also constantly changing.
If the operator sets the gap between the stripper blade and the feed roller surface too small, the pressure of the rubber in the feed section increases still further and the pressure on the stripper blade becomes disproportionately high. This phenomenon causes wear of the stripper blade to increase considerably.